Chapter 24: Organic chemistry

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Chapter 24 Organic chemistry
Chemistry 1062 Principles of Chemistry II Andy
Aspaas, Instructor
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Carbon

• Carbon central element of organic chemistry
• Organic compounds compounds containing
  carbon-carbon bonds
• 4 valence electrons 4 must be shared from other
  atoms
• 4 single bonds (tetrahedral)
• 1 double bond, 2 single bonds (trigonal planar)
• 2 double bonds (linear)
• 1 triple bond, 1 single bond (linear)

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Hydrocarbons

• Hydrocarbon molecule that contains only carbon
  and hydrogen atoms
• Saturated hydrocarbons only CC single bonds
• May be cyclic or acyclic
• Unsaturated hydrocarbons contain some
  carbon-carbon double and/or triple bonds
• Aromatic hydrocarbons contain benzene rings
• (Non-aromatic hydrocarbons are aliphatic)

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Alkanes and cycloalkanes

• Alkanes are acyclic saturated hydrocarbons
• Cycloalkanes are cyclic saturated hydrocarbons
• Molecular formula indicates only type and
  quantity of atoms in a molecule
• Structural formula indicates connectivity in the
  molecule (which atoms are bonded to which)
• Structural formulas look like Lewis structures
• Condensed structural formulas dont draw the
  bonds, but still indicate connectivity

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Straight-chain alkanes

• Straight-chain alkanes (or normal alkanes) have
  all carbons in a row
• n- at beginning indicates straight-chain (normal)
• General formula CnH2n2

Name Molecular formula Structural formula
Methane CH4 CH4
Ethane C2H6 CH3CH3
Propane C3H8 CH3CH2CH3
n-Butane C4H10 CH3(CH2)2CH3
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Straight-chain alkanes (5 C through 10 C)

• For straight-chain alkanes 5 C through 10 C, use
  Greek prefix followed by -ane

Name Molecular formula Structural formula
n-pentane C5H12 CH3(CH2)3CH3
n-hexane C6H14 CH3(CH2)4CH3
n-heptane C7H16 CH3(CH2)5CH3
n-octane C8H18 CH3(CH2)6CH3
n-nonane C9H20 CH3(CH2)7CH3
n-decane C10H22 CH3(CH2)8CH3
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Isomerism in alkanes

• n-Butane has a contsitutional isomer (same number
  and kind atoms, different bonds)
• Same molecular formula, different structural
  formula
• Isobutane branched, all carbons not in a row
• CH3(CH3)CHCH3 (parentheses mean group is not in
  the main chain)

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Branched alkanes

• More complex branched alkanes require different
  naming rules
• Any of the straight-chain alkanes can be made
  into substitutents - or branches off a main
  chain
• Methane becomes methyl as a branch (CH3)
• Ethane becomes ethyl as a branch (CH2CH3), etc

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Naming complex branched alkanes

• Start by identifying the longest carbon chain
• Identify branches off the longest chain as their
  substituent name (methyl, ethyl, propyl, etc)
• Number longest chain starting at end closest to
  the first branch
• Name the compound, starting with branches and
  indicating the number on the main chain to which
  the branch is attached

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Cycloalkanes

• Saturated hydrocarbons which form a ring of
  carbon atoms
• General formula CnH2n
• Prefix name with cyclo- and name as if straight
  chain
• E.g. cyclobutane (4 carbons) cyclohexane (6
  carbons)
• Any organic molecule can be drawn as a line-angle
  formula, where carbons and hydrogens are not
  explicitly shown.
• Line-angle drawing of cyclohexane is simply a
  hexagon
• Practice drawing!

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Alkenes and alkynes

• Alkenes and alkynes unsaturated hydrocarbons
• Typically more reactive than alkanes (reactions
  can occur at carbon-carbon double and triple
  bonds)
• Hydrogenation addition of two hydrogen atoms
  across a double bond
• Alkenes general formula CnH2n just like
  cycloalkanes
• Names end with -ene (compared to -ane ending of
  alkanes)

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Naming alkenes and alkynes

• Ethene is the simplest alkene (CH2CH2)
• Common name is ethylene
• When there are more than one possible place to
  put the double bond, its location must be
  indicated
• Start numbering carbons at end closest to the
  double bond, and indicate the lower-numbered
  carbon involved in double bond
• Ex. 1-butene CH2CHCH2CH3
• 2-butene CH3CHCHCH3
• Alkynes are named the same way, with -yne instead
  of -ene

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Aromatic hydrocarbons

• Benzene ring six-membered carbon ring with
  alternating single- and double-bonds

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Nomenclature of aromatic hydrocarbons

• For singly substitued benzenes, use substituent
  names and benzene as the suffix (ex.
  Methylbenzene, ethylbenzene, etc.)
• When 2 identical groups are substituted on a
  benzene, ortho-, meta-, and para- are used to
  differentiate the isomers
• Multiple substituents require the benzene ring to
  be numbered from 1-6 so that the substitutents
  get the smallest possible numbers

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Hydrocarbon derivatives

• Most organic molecules contain elements other
  than carbon and hydrogen
• Heteroatom atom thats not C or H in an organic
  molecule
• Functional group common grouping of atoms which
  reacts in a particular way
• Oxygen-containing functional groups are the most
  common

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Oxygen-containing functional groups

• Molecule fragments which symbolize
  oxygen-containing functional groups
• R and R symbols for general hydrocarbon groups

Alcohol Aldehyde
Ether Ester
Ketone Carboxylic acid
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Alcohols

• Alcohol ROH functional group
• Named with similar rules to hydrocarbons
• Main chain must contain carbon bonded to OH
• Suffix -ol on chain name
• Position of OH group indicated by number (omit
  if unnecessary)
• Ex. Methanol, ethanol, 2-propanol

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Ethers

• Ether ROR
• Common name list the two R groups and suffix
  with ether
• Ex. Methyl ethyl ether, diethyl ether
• IUPAC name alkoxy derivative of longer chain
• Ex. Methoxy ethane, ethoxy ethane
• Diethyl ether (or just ether) used as solvent,
  previously an anesthetic

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Aldehydes

• Aldehydes, ketones, carboxylic acids, and esters
  all contain a carbonyl group (CO double bond)
• Aldehyde carbonyl with a hydrogenattached
• Usually abbreviated CHO
• Methanal CH2O (common name formaldehyde)
• Ethanal CH3CHO (common name acetaldehyde)

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Ketones

• Ketone carbonyl with two hydrocarbon groups
  attached
• Abbreviated CO
• Named with -one suffix on stem name, number
  indication position of carbonyl
• Propanone CH3COCH3 (common name acetone)
• 2-butanone CH3COCH2CH3 (common name methyl
  ethyl ketone)

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Carboxylic acids

• Carboxylic acids contain a carboxyl group, COOH
• Named like aldehydes, but with-oic acid as
  suffix
• Many have common names
• CH3COOH ethanoic acid - vinegar (common name
  acetic acid)
• CH3(CH2)2COOH butanoic acid - rancid
  dairy(common name butyric acid)

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Esters

• Ester RCOOR
• Formed by reaction of alcohol with carboxylic
  acid
• Ex. Ethanol Acetic acid ? Ethyl acetate
• Pleasant, fragrant smells
• Many familiar fruit smells are esters

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Nitrogen-containing functional groups

• Amine RnNH3-n
• Generally sharp- or strong-smelling
• Ammonia NH3
• Triethylamine (CH3CH2)3N smells like dead fish

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Amides

• Amides RCONH2 or RCONHR
• Formed by reaction of amine with carboxylic acid,
  similar to ester formation